This invention relates generally to phacoemulsification devices and methods for liquefying and aspirating lens nuclei in vivo.
A cataract is an opacity or clouding of the lens, the elliptical, normally transparent structure that sits behind the pupil of the eye. The lens of the eye focuses light rays into images on the retina, the photosensitive tissue at the back of the eye. The lens of an adult human eye is about 9 millimeters in diameter and about 5 millimeters thick. The lens consists of an inner nucleus and an outer cortex; it is surrounded by a cellophane-like capsule which is the basement membrane of the lens epithelial cells. In young people the lens is elastic and changes shape easily, allowing the eyes to focus clearly on both nearby and distant objects. Aging and other factors may cause the proteins of the lens nucleus to clump together, forming opaque (cloudy) areas known as nuclear cataracts.
According to the World Health Organization, cataracts are the leading cause of blindness around the world; an estimated 17 million people are blind because of them. In the U.S., where surgery has greatly reduced this risk, tens of thousands still lose their sight from this condition, and millions more have poor vision because of cataracts.
A typical procedure for treating cataracts is called extracapsular cataract extraction, in which the surgeon removes the central portion (the nucleus) of the lens but leaves the capsular bag in place, which adds structural strength to the eye and enhances the healing process. Less commonly, in intracapsular cataract extraction, the surgeon removes the lens and the entire capsule. There are greater risks with this procedure for swelling and retinal detachment. In both procedures the ophthalmologist works under an operating microscope to make a small incision in the cornea of the eye and then extracts the clouded lens through this incision; a replacement lens is then usually inserted.
With the clouded lens removed, the eye cannot focus a sharp image on the retina, and a replacement lens is needed. In about 90% of cataract operations an artificial lens, known as an intraocular lens (IOL), is inserted. In the remaining 10%, a new lens is not implanted; rather, the patient relies solely on corrective eyeglasses or contact lenses. During the most common cataract operations, the surgeon inserts the artificial lens into the capsular bag where the natural lens used to be.
In extracapsular lens removal, the anterior portion of the capsule is cut open so that the cataractous lens can be removed. However, the equatorial and posterior portions of the lens capsule are left intact. Once the cataractous lens nucleus and cortex are removed, the implant can be inserted therein. In traditional extracapsular cataract extraction, the lens nucleus is removed manually. A drawback of this is that a relatively large incision (from 8 mm to 11 mm) must be made in the limbus in order to remove the cataractous lens. That large of an incision causes a relatively lengthy post-operative healing time and is often the cause of significant surgically-induced post-operative astigmatism.
Ultrasonic phacoemulsification (phaco means lens), a version of extracapsular surgery, is now the most common cataract procedure in the United States. The ophthalmologist removes the clouded lens by using ultrasound to break it up into fragments so small they can be aspirated out with a suction device. A replacement lens is then usually inserted. The incision is much smaller than that made in conventional surgery and may not require a suture if the opening is watertight. A suture may be required if a tear or break occurs during the procedure or if an unfoldable lens is inserted that requires a wider incision.
In ultrasonic phacoemulsification the ultrasonic tip, which is rather sharp and made of metal, vibrates approximately 40,000 times per second in order to break up the lens nucleus into tiny pieces so that these pieces can then be aspirated from the eye. The advantage of phacoemulsification is that it allows lens nucleus removal through a relatively small incision of about 3 mm. The disadvantage, however, is that it has proven to be relatively dangerous since the ultrasonic tip destroys any and all tissue that gets in its way. If the vibrating tip comes into contact with the cornea, iris, or capsule, it can cause serious and permanent damage. Moreover, during the break up of the hard nucleus, the tip may contact with and tear the posterior capsule. Another disadvantage of phacoemulsification is that it requires a very high degree of skill, concentration and experience on the surgeon""s part for it to be performed well on a consistent basis.
Due to the above, cataract surgeons desire a small incision cataract extraction procedure which is inherently safer and easier to perform than phacoemulsification. U.S. Pat. No. 5,616,120 to Andrews et al. describes a technique for liquefying a hardened cataractous lens by injecting hot water or saline into the capsular bag for emulsification of a cataractious lens within the bag. Once the hot solution heats and liquefies the nucleus, one is able to aspirate the lens and insert a new intraocular lens. The invention has the disadvantage of jetting hot water across the capsule with potential damage to other structures such as zonules and the endothelium.
Therefore, it is an object of the invention to provide a method and apparatus for safely liquefying the hardened nucleus of a lens, so as to allow its removal by aspiration.
It is a still further object of the invention to provide a simplified appartus with which to perform phaocemulsification and aspiration of lens nuclei, to reduce the possibility of accidents and surgeon error.
It is another object of the invention to use heat in order to safely liquefy a hardened lens nucleus before its eventual aspiration.
The present invention achieves these objectives by localized heating along the edge of an aspiration cannula. The cannula is initially inserted through a small incision in the cornea, or in the limbus, and contacted with the lens. An electrically resistive element is fixed to the tip of the cannula, and generates heat when electricity is passed through it. The heat irradiates the lens, raises the temperature of the lens tissue, and liquefies the lens. Upon liquefication the lens is aspirated.
In accordance with the purpose(s) of this invention, as embodied and broadly described herein, this invention, in one aspect, relates to a phacoemulsification and aspiration device comprising: (a) a substantially hollow housing comprising a first end and a second end; (b) an electrical resistance heating element disposed at the first end of the housing and configured to thermally irradiate a space proximal to the first end and exterior to the housing; (c) a source of electricity in electrical contact with the heating element; and (d) a vacuum source disposed at and integrally connected to the second end of the housing.
In another aspect the invention relates to a method for treating cataracts in vivo by liquefying a cataractous lens nucleus and aspirating the same from within a surrounding lens capsule comprising the steps of: (a) thermally irradiating and liquefying a lens; and (b) aspirating the lens.
Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.